1. Field of the Invention
The present invention relates to camera multi-mode exposure control devices and more particularly to such devices for selecting an exposure control mode and setting exposure conditions for the multi-mode exposure control device.
2. Description of the Prior Art
Multi-mode exposure type cameras have been proposed which offer shutter-speed priority, diaphragm-aperture priority and programmed automatic exposure controls as well as manual exposure control. Such cameras automatically control diaphragm aperture, shutter speed or the combination of the two in accordance with a measured scene brightness and previously set exposure parameters, such as a shutter-speed value in the case of the shutter speed priority automatic mode, a diaphragm aperture value in the case of the diaphragm-aperture priority automatic mode, and a film speed value in the above three cases. With such multi-mode exposure type cameras, the camera operator can photograph in any desired one of the exposure control modes. The multi-mode exposure control is often employed in single lens reflex (SLR) cameras to increase their versatility.
With the diaphragm priority mode selected in such SLR cameras, the diaphragm is stopped-down to a manually preset value in response to the shutter release operation. This is followed by retraction of the reflex mirror from the photographic optical path and subsequent release of the leading shutter curtain. The trailing shutter curtain is released to start travelling after a lapse of time which is controlled in accordance with the output of a first light receiving element which in turn receives the scene or object light passed through the camera objective and reflected from the surface of the leading shutter curtain which has a reflection index that is substantially identical to that of the film surface.
When the shutter speed priority mode is selected, the light measurement is made by a second light receiving element which receives the scene light passed through the camera objective, with the diaphragm aperture stopped-down, and then reflected by the reflecting mirror. When the value of the light measurement as a function of the output of the second light receiving element reaches a predetermined value relative to a manually preset shutter speed value and the film sensitivity value, the diaphragm stopping-down operation is interrupted to thereby automatically determine the diaphragm. aperture. After the reflecting mirror has retracted from the optical path, the scene light passed through the automatically determined diaphragm aperture and then reflected by the surface of the leading shutter curtain and/or film surface at the camera focal plane is measured by the first light receiving element to control the actuation of the trailing shutter curtain for exposure termination.
Further, when the programmed automatic control mode is selected, exposure operation is performed with a specific combination of a shutter speed and a diaphragm aperture that is automatically selected from a programed set or series of combinations, in accordance with a measured scene brightness and a set film sensitivity. The program for such an exposure control may be represented by a line in a graph with parameters of shutter speed, diaphragm aperture and exposure value. In the case of the manual mode, both the shutter speed and the diaphragm aperture are determined in accordance with manual settings.
Prior art multi-mode exposure control cameras generally require the camera operator to perform at least two manual operations on handling members for the mode selection and the exposure parameter setting. For example, if the camera operator wants the diaphragm-aperture priority mode, he must at first operate a mode selection member to select the diaphragm-aperture priority mode, and then operate a diaphragm setting member to select a desired diaphragm-aperture value. Additionally, prior art multi-mode exposure control cameras often require that the manual setting member, for the exposure factor that is to be controlled automatically, is set to a specific position. For example, a manual shutter speed setting member may have to be set to a specific, e.g. an automatic, position upon selection of the diaphragm-aperture priority mode wherein the shutter speed is automatically controlled in accordance with a measured scene brightness, a set film sensitivity as well as a set diaphragm aperture. Likewise, a manual diaphragm aperture setting member may have to be set to a specific position, e.g. the minimum aperture, i.e. the maximum f-number position, upon selection of the shutter speed priority mode. Even for the program mode wherein both the diaphragm aperture and the shutter speed are automatically controlled, manual operation of the diaphragm aperture and/or shutter speed setting members is often required in addition to the operation for the mode selection.
Thus, the prior art multi-mode cameras are inconvenient for handling and difficult for use, especially by amateurs and beginners, because of the complexity and troublesomeness of various selecting and setting operations, in spite of the versatility and the convenience of automatic exposure control.
One approach to simplify the operation of the multi-mode camera is proposed in a Japanese laid-open patent application No. Tokkai-Sho 54-138431, published on Oct. 26, 1979 (corresponding to a U.S. patent application Ser. No. 29,919 assigned to the same assignee as the present application). The proposed camera is provided with a mode selection member for the selection of the shutter speed priority, diaphragm aperture priority and program modes, a pair of push buttons for exposure parameter setting and another push button for resetting the exposure parameter setting. With this camera, when the diaphragm aperture priority mode is set or selected, the value of the diaphragm aperture to be manually controlled changes, for example, to a smaller or minimum aperture size i.e. maximum f-number value, in response to the operation of one of the pair of push buttons. If the other push button is operated, the diaphragm aperture value changes oppositely than that just described. If the reset button is operated with the above mentioned diaphragm setting, the set diaphragm aperture value is reset and the camera is automatically switched to the program mode. When the shutter speed priority mode is selected, the shutter speed value is set and changes in response to the operation of either of the pair of push buttons. Operation of the reset switch resets the shutter speed setting and switches the camera to the program mode. Thus, the program mode is set only by the operation of the reset button. However, the mode selection member and at least one of the push buttons have to be operated upon switching from the diaphragm aperture priority mode to the shutter speed priority mode, or vice versa. In this case, at least two manual members have to be operated.